Heavy duty gas tube with a magnetic trigger



Dec. 28, 1965 v. JOSEPHSON HEAVY DUTY GAS TUBE WITH A MAGNETIC TRIGGER Filed June 6, 1962 [59/1 44 JOSE A SO/V I NVEN TOR.

BY QMP M .4770G/VE/ United States Patent 3,226,591 HEAVY DUTY GAS TUBE WITH A MAGNETIC TRIGGER Vernal Josephson, Palos Verdes Estates, Calif., assignor to The Aerospace Corporation, Los Angcles, Calif, a corporation of California Filed June 6, 1962, Ser. No. 200,436 4 Claims. (Cl. 313-154) This invention relates to a heavy duty switch and more particularly to a low inductance, low loss, heavy duty gaseous spark gap switch.

Switches are available for many types of electrical and electronic operations. Moreover, various operations require different types of switches for most effectively accomplishing a necessary switching operation. In the art of high power radar modulators and high current discharge devices there is a recognized need for very low inductance, low loss, high current capacity switching devices. Three common forms of switches presently in use in this art are hydrogen thyratrons, mercury ignitrons and spark gaps. Available hydrogen thyratrons are usually bulky, inductive and of limited current carrying capacity. Mercury thyratrons are less inductive but, initially, are resistive. Prior art spark gaps, although amenable to low inductance (coaxial) design have a finite minimum inductance and resistance due to the small size of the magnetically pinched current arc. Because of these problems, there is a recognized need for an improved low loss, low inductance, heavy duty switch.

Therefore, an object of the present invention is to provide a new and improved spark gap switch arrangement operable as a precisely controllable heavy duty, low impedance switch.

In connection with one embodiment of my invention, a pair of hollow planar electrodes are spaced apart with a low pressure hydrogen atmosphere therebetween. The support of the electrodes isolates them electrically. The spacing of the electrodes is less than that necessary for ionization and breakdown to occur at the operating voltages and pressures used. However, ionization and breakdown are triggered by providing, by means of a rapidly rising magnetic field, an orbital electric field, E0, such that free electrons describe paths long enough and with sufficient energy for ionizing collisions to occur and initiate maximum current flow. The magnetic trigger field is generated by a pulse coil juxtaposed to one electrode surface, and the electrode surfaces are provided with radial slits to prevent shunting of the magnetic triggering field. Once ionization has been initiated and a high current flow developed between the electrodes, the current flow tends to be pinched to a small radius, thus increasing the current density, arc inductance and dissipation. The contraction of the pinched current effect can be 211- leviated by the insertion of a permanent axial magnetic field arranged so that it does not impede current flow between the electrodes.

The subject matter which is regarded as this invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, as its organization and operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a plan view in cross-section of one embodiment of my invention:

FIG. 2 is a cross-sectional view taken along the line of 22 of FIG. 1:

FIG. 3 is a schematic circuit diagram illustrating one utilizing circuit arrangement of the present invention; and

Patented Dec. 28, 1965 FIG. 4 illustrates another embodiment of my invention.

Refering now to the drawing, wherein like numbers refer to similar parts, there is shown in FIG. 1 a pair of electrodes 10 and 11 having planar mating surfaces. These electrodes are connected by a coupling means such as lead wires 12 and 13 respectively to a high current capacity load network. Alternatively a fluid contacting the electrodes 10 and 11 can be made conductive whereby the leads 12 and 13 may be omitted. An outer metallic sleeve 15 surrounds the electrodes 10 and 11 and additionally shields the electrodes. The sleeve '15 also functions as the outer conductor of a low inductance coaxial cable arrangement.

The electrodes 10 and 11 are supported in a spaced parallel relationship by a hollow cylindrical insulating support 16 which confines there between a low pressure ionizable atmosphere such as hydrogen with the pressure being about 0.1 mm. Hg. Hydrogen at this pressure, although containing a few free electrons, will not be ionized by the operating voltages contemplated in the present invention. Therefore, energization or triggering of the switch 10-11 is accomplished by the application of a pulse 17 (FIG. 2) to a trigger coil 18 which is positioned adjacent to the electrode surfaces. In order that the triggering magnetic field provided by the trigger coil 18 is not shunted, the mating surfaces 20 and 22 of the electrodes 10 and 11 respectively are provided with radial slits 28 (FIG. 2) which extend about half way toward the rear portion of these electrodes (FIG. 1). In order to further eliminate shunting of the triggering field generated by the trigger coil 18 the sleeve 15 is provided with axial slits 33. These slits 33 also function to facilitate assembly of the spark gap switch 10-11.

In order to prevent energized particle traversal of the hollow portions of the electrodes 10 and 11 a second pair of receiving surfaces 24 and 26 is provided directly below the slits of the electrode surfaces respectively. As is shown more clearly in FIG. 2 the slits 28 in the outer surface of the electrode 11 are misali ed compared to the slits 30 in the inner receiving surface 26. Thus, escape of particles, etc., is substantially eliminated, and particle bombardment of the trigger coil 18 is prevented. As an alternative construction, the receiving surfaces may be omitted and the slits 28 filled with a suitable material such as ceramic.

Subsequent to ionization and breakdown between the electrodes 10 and 11, the current flow contemplated is sufficiently large to tend to induce substantial pinching of the plasma column. Such pinching, by the induced magnetic field, reduces the plasma column to a small radius, and thus increases the current density, are inductance and dissipation. I have provided a means for reducing this pinch effect in the form of a permanent axial magnetic field within the conducting plasma. As illustrated in FIG. 1 this field is provided by a ring magnet 32. Such an axial field reduces the pinch effect without impeding current fiow between the electrodes 10 and 11.

Refering now to FIG. 3 I have shown a simplified chematic circuit diagram illustrating a typical connection arrangement for the spark gap switch 10-11. The trigger pulse 17 is developed by a simple pulse current wherein a capacitor 35 is charged to a high B+ voltage through a load resistor 36. At the instant the trigger pulse 17 is desired, a gas discharge device 38 is fired to drop the voltage of the capacitor to ground potential and thus establish the triggering voltage pulse 17.

The load utilization circuit of the spark gap switch 10-11 is illustrated schematically by a load circuit illustrated for convenience as a resistor 40 coupled in circuit with the switch 1011 and a large capacitor 42. Prior to triggering the load circuit, the capacitor 42 is charged to store a substantial amount of energy through a resistor 44 connected to a B+ voltage source.

Triggering of the spark gap switch 10-11 shunts the current stored in the capacitor 42 through the load 40. Typically, when the capacitor 42 has been charged to 25 kilovolts the time lag between the trigger pulse 17 and full conductance of the order of 30,000 amperes through the switch 10-11 is about .4 microsecond. As the maximum voltage of the charge is reduced using a particular configuration, the time delay increases slightly whereby at 10 kilovolts the time delay is .6 microsecond, at 5 kilovolts the delay is 1 microsecond and at 2 kilovolts it is 2.5 microseconds.

This operation is typical for an arrangement of my invention wherein the diameter of the mating surfaces of the electrodes and 11 is substantially greater than the gap therebetween. Thus, with a gap of 1 centimeter and an electrode diameter of 6 centimeters the above operation results in a virtually jitter free breakdown in the delay times specified above. On the other hand, with a 1 centimeter gap utilizing only 4 centimeters electrode diameter the maximum voltage obtainable across the switch 10-11 (with other parameters the same) is less than 25 kilovolts. Obviously, many configurations may be designed to provide desired maximum operating voltages and predetermined trigger to breakdown time delays.

Referring now to FIG. 4, I have shown another embodiment of the present invention. A major change between the FIGS. 1 and 4 is the relocation of the trigger coil 18' which is now placed outside an insulating support 16'. Also, in the particular construction illustrated in FIG. 4 the electrodes 10 and 11' are chamfered at their mating periphery surfaces 46 and the lead wires 12' and 13' are of a substantially larger. diameter whereby the ratio of their diameter to that of the sleeve 15 approaches unity to reduce to a minimumthe inductance of the coaxial arrangement, as is well known in the coaxial art.

The arrangement of the insulating support 16' is such that an annular detent 48 projects inwardly between the chamfered surface 46 to prevent any scattering of the current flow which scattered current flow would result in relatively long current paths between the mating surfaces of the electrodes 10' and 11. In the embodiment of FIG. 4 I have also provided a permanent axial magnetic field producing means for reducing the pinch affect as discussed above in connection with FIG. 1 in the form of coil 32a. The use of the coil 32a, although requiring additional power, avoids any problem of heat damage to a permanent magnet. Also, in the embodiment of FIG. 4 I have provided radial slits 28 in the electrodes 10' and 1'1 and axial slits 33 in the sleeve 15, to prevent shunting of the trigger field.

While I have shown and described particular embodiments of the present invention, further modifications may occur to those skilled in this art. I desire it understood, therefore, that my invention is not limited to the particular form illustrated and I intend by the appended claims to cover all such modifications which do not depart from the true spirit and scope of my invention.

I claim:

1. A spark gap switch comprising:

a pair of electrodes having spaced apart mating planar surfaces of a diameter substantially greater than the space therebetween;

insulating means for supporting said pair in such spaced apart relation and for maintaining there- 4, between an atmosphere of an ionizable gas, the potential across said pair of electrodes being normally less than that necessary to ionize and breakdown said atmosphere;

means for generating a magnetic pulse field in the region between said pair of electrodes to ionize and breakdown said atmosphere, said pair of electrodes being of a configuration which will not shunt said pulse field; and

means for developing a magnetic field to inhibit induced pinch effect in the current flow between said pair after ionization and breakdown.

2. A spark gap switch comprising:

a pair of electrically isolated electrodes having opposing plane circular surfaces supported in spaced apart relation, the spacing between said pair being a fraction of the diameter thereof;

means maintaining a low pressure gaseous atmosphere between said surfaces, said pressure being such that the atmosphere remains nonconductive in the presence of a high potential across said pair;

means for generating a magnetic trigger pulse field in the region between said pair to ionize and breakdown said atmosphere, said pair of electrodes each having radial slots therein to prevent shunting of said trigger field; and

means inhibiting pinch effect on the current flow between said pair.

3. A spark gap switch comprising:

a pair of electrodes having spaced apart opposing planar surfaces of a diameter substantially greater than the spacing therebetween;

insulating means for supporting said pair in such spaced apart relation and for maintaining therebetween a gaseous atmosphere, said arrangement being able to have developed across said pair a voltage of the order of several kilovolts without ionization and breakdown;

a trigger pulse coil in the region of said opposing surfaces for generating a magnetic pulse field between said pair to ionize and breakdown said atmosphere, said pair of electrodes being radially slotted toprevent shunting of said pulse field; and

means providing a magnetic field counteracting pinch effect in the current path between the pair of electrodes.

4. A spark gap switch comprising:

a pair of electrically isolated electrodes having opposed surfaces supported in spaced apart relation;

means maintaining a low pressure gaseous atmosphere between said surfaces, said pressure being such that the atmosphere is normally nonconductive in the presence of a high potential across said pair;

means for generating a magnetic trigger pulse field between said pair to ionize and breakdown said atmosphere; and

means producing a constant magnetic field inhibiting pinch effect on the current flow between said pair.

References Cited by the Examiner UNITED STATES PATENTS 1,328,041 1/1920 Fischer 313161 X 1,617,180 2/1927 Smith 313-l61 X 1,714,405 5/1929 Smith 313161 2,966,601 12/1960 Peek 313-161 X GEORGE N. WESTBY, Primary Examiner.

BENNETT G. MILLER, Examiner. 

4. A SPARK GAP SWITCH COMPRISING: A PAIR OF ELECTRICALLY ISOLATED ELECTRODES HAVING OPPOSED SURFACES SUPPORTED IN SPACED APART RELATION; MEANS MAINTAINING A LOW PRESSURE GASEOUS ATMOSPHERE B ETWEEN SAID SURFACES, SAID PRSSURE BEING SUCH THAT THE ATMOSPHERE IS NORMALLY NONCONDUCTIVE IN THE PRESENCE OF A HIGH POTENTIAL ACROSS SAID PAIR; 